Orthodontic treatment mainly consists of a period of active treatment and a period of inactive treatment. In the period of active treatment the teeth concerned and their connective tissues are moved to the target positions in the jaw(s). The period of active treatment is then followed by a period of inactive treatment, also referred to as the retention period, during which the teeth concerned and their connective tissues are sought to be stabilized, or retained, in the positions obtained. Therefore, in the retention period orthodontic patients must wear suitable retainers 24 hours or part of it a day for up to several years, in order thereby to ensure that the tooth positions obtained are maintained over time.
Known retainers comprise removable retainers and fixed retainers.
A removable retainer is formed essentially of plastic-based retainer plates, which are often combined with steel braces and steel clamps. Said steel components can either be used as independent retainer elements, or as securing devices or as reinforcement to brace and thereby reinforce said retainer plates. The removable retainer is used during parts of the day, which means that the patient must be instructed on the use and maintenance of the retainer.
A fixed retainer is essentially formed of orthodontic wire, also called retention wire, the wire being cut into suitable lengths and adapted for the pair of teeth or segment of teeth in question. The orthodontic wire can vary in type, including individual wire or twisted wire; in cross-section, including round, square or rectangular cross-sections; and in type of metal(s) or alloys.
The wire can either be attached directly to the teeth by a suitable dental bonding material, e.g. composite material, in the form of small lumps of glue or, as earlier, in that the wire is soldered to orthodontic strips enclosing the anchoring teeth concerned, the orthodontic strips being secured to the anchoring teeth by means of a suitable bonding material. Alternatively, the fixed retainer may be formed of an integral moulded brace, a bar, with associated fasteners, so-called retention bases, which are secured to the anchoring teeth concerned by means of suitable bonding material.
Fixed retainers are preferably used on the inside of the dental arch at the front of the lower jaw (lingually) and to a somewhat lesser extent on the inside of the dental arch at the front of the upper jaw (palatinally).
To achieve a good result by the use of a removable retainer, one is completely dependent on the patient's will and ability to cooperate and maintain the retainer correctly. Moreover, retainer plates are inaccurate in the sense that over time they do not maintain the exact tooth position, so that limited tooth setting must be counted on. Besides, the plates can be uncomfortable to wear and be prone to break easily, which makes removable retainer plates unsuitable for retention lasting several years.
The use of a fixed retainer results in disadvantages in the dental hygiene and may, when dental-hygienic means are used, lead to inadvertent breakage between tooth and bonding material. As mentioned, fixed retainers are preferably used at the front of the lower jaw, tooth positions in this region of the set of teeth normally being more unstable than other regions of the set of teeth, the lingual area at the front of the lower jaw forming at the same time the primary region of deposits of plaque and formation of tartar.
A fixed retainer extends continuously from tooth to tooth in the tooth region covered by the retainer, thus preventing normal dental-hygienic use of dental floss or toothpicks. The use of dental floss is prevented in that the dental floss cannot be inserted in a normal manner between two adjacent teeth in order to clean the tooth neck area, or the cervical area, between the teeth. When dental floss is used, the patient has to insert the dental floss underneath the retention wire, an action which is technically difficult to perform, and which thereby represents a practical disadvantage. On the other hand, the use of toothpicks to clean between the teeth is easier for the patient to carry out, but the use of toothpicks may at the same time lead to serious disadvantages. When the toothpick is inserted between the teeth, the teeth are pushed, or expanded, away from each other to some degree, so that the applied expansion force stretches the retention wire(s) and stresses the anchoring points of the wire(s). The bonding material between the wire(s) and the teeth may thereby break and come loose, so that the entire retainer, or parts of it, come(s) loose from the teeth that are sought to be stabilized. Moreover, the use of toothpicks in children and juveniles may cause damage to the hard and soft tissues and is therefore not recommended for this group of patients.
When fixed retention wires are used, the desired tooth positions are secured best when the wire is glued to each tooth in the involved group of teeth, or retention segment, which is sought to be stabilized. However, it is often the case that the retention wire comes loose from one or more of the anchoring points, and this may be difficult to discover for both the patient and the dentist. Often this will not be discovered until the teeth concerned have moved away from the desired tooth positions, to a larger or smaller degree. This results in an immediately poorer result of treatment and a much poorer long-term prognosis for the stabilization of the occlusion.
A retention wire is normally secured to a tooth by means of a composite material. This is carried out in such a way that sufficient amounts of composite material are applied round the retention wire and on the surfaces of the individual anchoring teeth, and so that after hardening, the composite material appears as lumps of glue of varying extent and projection on the dental surfaces. This represents a further drawback, as the surfaces of the glue lumps, which are somewhat porous and rough, form surfaces that are suitable for plaque to accumulate on and subsequently tartar to form.
The disadvantages connected to reduced hygienic accessibility and fixed retainers inadvertently coming loose, increase in adult patients, in whom the requirements to good dental hygiene and long-term retention are stricter than what is normally the case in children and juveniles.